1. Field of the Invention
The present invention relates generally to thermostatic control of cooling fluids, and more particularly, but not by way of limitation, to an improved method and apparatus for controlling the temperatures of individual mold zones heated by repeated cycles of high pressure injection of molten metal or plastic into mold impressions, by controlling the flow of outgoing coolant using precisely calibrated, temperature sensitive, flow control thermostatic control valve at individual cooling channels.
2. Brief Description of Related Art
To control heat transferred into molds by molten metal or plastic used in molding processes, individual impression areas and components are cooled by separate cooling channels drilled through the impression material. These channels are plumbed to an intake manifold and an exhaust manifold.
Mold impression temperatures have a significant impact on production cycle times and cast part quality. Practical, reliable, and economical control of impression temperatures is normally limited by the design (size and location) of individual cooling channels. Quality mold designs use central manifolds to supply cooling water into the die, and separate manifolds fitted with ball valves to receive heated outgoing coolant water. This design minimizes complexity and reduces production setup time by providing one main connection at each side of the mold cooling system.
Ball valves are often used on the exhaust side cooling manifold to control the flow rate of coolant through the cooling channels to refine temperatures of the coolant; increasing flow reduces coolant and mold temperatures, while restricting flow acts to increase temperatures by exposing the coolant to the heated die steel for a greater period of time. This is the most common, reliable, and economical method for temperature control once the sizes and locations of the cooling channels have been established.
The shortcoming of the ball-valve system is that a valve setting is only valid if all process variables remain the same (e.g., the same amount of BTU's are put into the mold). Metal temperatures, cycle time, spray quantity and duration, hold times and other variables can fluctuate and significantly change the amount of heat introduced into the mold. To control coolant/steel temperatures properly, the control method must measure and accommodate (modulate) changes in the process in order to maintain a stable production process.
While methods for controlling mold temperatures automatically have been proposed, such methods involve the restricting the flow of coolant on the intake side of the mold. When using a coolant control method that restricts flow, the flow of coolant should be controlled on the exhaust side of the mold so as to control the flow of coolant exiting the mold. Flow should not be restricted on the intake side of the mold as it may result in an under supply of coolant to the cooling channels and cause mold problems related to overheating of the coolant. Overheating coolant can result in overheating/damage of die steel and coolant boiling which may deposit undesirable mineral scale within the lines that act as an insulator, further reducing cooling efficiency and overheating problems.
To this end, a need exists for an improved method and apparatus for controlling the temperatures of individual mold zones heated by repeated cycles of high pressure injection of molten metal or plastic into mold impressions, by controlling the flow of outgoing coolant using precisely calibrated, temperature sensitive, flow control thermostatic control valves at individual cooling channels. It is to a method and apparatus that the present invention is directed.